The instant invention relates to depositing n-type and p-type ZnO-based transparent conducting oxides (TCO) at low temperatures (e.g., by plasma enhanced chemical vapor deposition (PECVD)) by using a mixture comprising at least one volatile organometallic zinc compound such as diethyl zinc (DEZ), at least one diluent gas such as argon or helium, at least one oxidant such as carbon dioxide and usually at least one volatile dopant or reactant. By using a relatively low deposition temperature, the inventive process permits depositing doped ZnO, ZnO co-deposited with other elements, Zn alloyed with other elements in oxide form on glass and temperature sensitive materials such as plastic and polymers. The inventive process achieves desirable electrical and optical properties of the doped, co-deposited or alloyed ZnO that permits deposition upon relatively rigid and fragile glass substrates used in many applications such as flat panel display. The inventive process can also permit replacement of glass substrates with relatively flexible and durable plastic or polymer substrates.
Undoped ZnO has been deposited on a wide variety of substrates at low temperatures by physical vapor deposition techniques such as sputtering and ion plating. Undoped ZnO can also be deposited on a substrate at low temperatures by PECVD using a mixture of organometallic zinc compound and oxygen, N2O, or CO2.
Doped ZnO films such as n-Type ZnO films co-deposited with Group III elements such as Al, Ga, Tl, Y, Sc, or In, and Group IV elements such as Ge, In, Sn, Ti, Zr, Pb or Hf and p-type ZnO with oxide of Group V element such as Sb, P, As, Bi, V, Nb, or Ta have been deposited on a wide variety of substrates at low temperatures by physical vapor deposition techniques such as sputtering and ion plating. The ZnO films co-deposited with above-mentioned elements have been shown to have useful electrical and optical properties. However, the growth rate of the doped ZnO films deposited by conventional physical vapor deposition techniques is ineffective.
B or Al-doped zinc oxide or ZnO mixed with oxides of other metals with good electrical and optical properties has been deposited at low temperatures by PECVD using a mixture of volatile zinc compound, boron compound as a dopant, and water, oxygen or nitrous oxide (N2O) as an oxidant. If an organo-zinc complex (e.g., DEZ) is mixed either with water vapor, oxygen or N2O, the complex instantaneously forms a solid, thereby contaminating the feed line as well as the substrate to be deposited by ZnO. Because a volatile zinc compound such as diethyl zinc or dimethyl zinc reacts violently with water vapors, oxygen or N2O well below the deposition temperatures, the reactants are introduced into the deposition chamber via separate lines. Since introducing reactants via separate feed lines makes it difficult, if not impossible, to achieve homogeneity of mixing and delivery of reactants uniformly to the substrate, it is difficult to deposit doped ZnO or ZnO mixed with oxides of other metals with good quality consistently and uniformly. This also prevents that process from depositing doped ZnO or ZnO mixed with oxides of other metals on large area substrates.
There is a need in this art for a process that is suitable for depositing low-resistivity doped ZnO for TCO application at low temperatures.